Phenol is produced through a step of oxidizing alkylbenzene to alkylaryl hydroperoxide, a step of concentrating an oxidation reaction product of alkylbenzene, a step of subjecting the concentrated solution to cleavage into phenol and a ketone with an acid catalyst, a step of neutralizing the acid cleavage product, and a step of separating the acid cleavage product by distillation.
As a process for producing phenol, for example, a process for acid decomposition of cumene hydroperoxide obtained by oxidation of cumene is well known. The acid decomposition product in this process contains, in addition to phenol and acetone as main components, various by-products such as α-methylstyrene, acetophenone, cumylphenol, 2-phenyl-2-propanol (also called α-dimethylphenyl carbinol) and unreacted cumene, and various carbonyl compounds such as a trace amount of hydroxyacetone (HA) and α-phenylpropionaldehyde (α-PPA). In the application of phenol, an example of which is polycarbonate manufactured from diphenylolpropane (also called bisphenol A) as a raw material, high-purity phenol is required.
For such a high purity phenol, it is necessary that the content of hydroxyacetone (HA) as an impurity is reduced to 30 ppm or less, preferably 10 ppm or less. In addition, it is necessary that the total amount of other aliphatic and aromatic carbonyl compounds contained, i.e., total amount of carbonyl compounds other than HA, is reduced to 100 ppm or less, preferably 50 ppm or less. In order to obtain such a high-purity phenol, purification is carried out, wherein most of the low-boiling substances such as acetone, cumene, water and α-methylstyrene, and most of the high-boiling substances such as acetophenone and 2-phenyl-2-propanol are removed from a neutralization product of the acid decomposition product by means of fractional distillation to give a phenol fraction, and further the aliphatic carbonyl compounds such as hydroxyacetone, and the aromatic carbonyl compounds such as α-phenylpropionaldehyde are removed from the phenol fraction. However, it is particularly difficult to remove those carbonyl compounds from phenol, which thus deteriorates the quality of phenol as a product.
For a conventional process for producing high-purity phenol, for example, JP-B No. 37-11664 (Patent Document 1) proposes a process in which hydroxyacetone and phenol are subjected to react by bringing crude phenol (content of hydroxyacetone: 200 ppm) into contact with an activated alumina catalyst at 360° C. to give 2-methylbenzofuran (2-MBF), and phenol and 2-methylbenzofuran are then separated by means of steam distillation. In addition, JP-B No. 54-1289 (Patent Document 2) discloses a process in which activated alumina is used for the purification of cresol. In addition, JP-B No. 42-12250 (Patent Document 3) proposes a process which comprises bringing crude phenol into contact with a silica/alumina catalyst at 150 to 250° C. to convert carbonyl compound as an impurity to another compound, and separating the compound and phenol by distillation. Moreover, GB Patent No. 1231991 (Patent Document 4) proposes a process which comprises bringing crude phenol containing no water into contact with an acidic ion exchange resin catalyst at 80 to 150° C. to convert carbonyl compound as an impurity to another compound, and then separating the compound and phenol by distillation.
However, the above methods cause a problem such that the efficiency of the removal of impurities is insufficient, or that phenol and α-methylstyrene, which are useful components in the crude phenol, react with impurities, or each of them undergoes addition reaction with the other or independently to produce cumylphenol or olefin dimers, and thus the useful components are lost.